FastMetal

Model comparison

GPT-6.1 Sol vs GPT-6 Luna

Pricing, context window and real answers (September 2026)

GPT-6.1 Sol (OpenAI) and GPT-6 Luna (OpenAI), compared as you can actually call them on FastMetal. Both are served from the same OpenAI-compatible endpoint and API key; switching is a change to the model string.

Specs and pricing

openai logoGPT-6.1 Solopenai logoGPT-6 Luna
ProviderOpenAIOpenAI
Input (per 1M tokens)¥357.4¥17.87
Output (per 1M tokens)¥1,787¥89.35
Typical cost (1,000 in + 500 out tokens × 1,000 calls)¥1,251¥63
Context window1,050,000 tokens1,050,000 tokens
Release date9/29/20269/22/2026
Input modalitiesfile, image, textfile, image, text
Throughput (p50)——
Arena · overallUnranked#86 · ELO 1,442
Arena · JapaneseUnrankedUnranked
Arena · codingUnranked#43 · ELO 1,515

Prices are FastMetal's yen rates before tax.

Rankings: LMArena leaderboard dataset (lmarena-ai/leaderboard-dataset), CC BY 4.0, snapshot 2026-09-25; category names mapped and ratings rounded by FastMetal.

Which should you pick?

  • On price, GPT-6 Luna: ¥89.35 per 1M output tokens, 95% less than GPT-6.1 Sol.
  • If in doubt, try both on the same key. Switching is a change to the model string, and each is billed at its own rate.

Real answers to the same prompts

Exactly what the FastMetal gateway returned, side by side. Not benchmark scores: actual output.

Count the number of 'r's in 'strawberry'

Count the number of 'r's in 'strawberry'. Explain your reasoning step by step.

GPT-6.1 Sol

“strawberry” is spelled **s-t-r-a-w-b-e-r-r-y**. The letter **r** appears at positions **3, 8, and 9**. So, there are **3 r’s** in “strawberry.”
2.8s88 output tokens

GPT-6 Luna

In **“strawberry”**, the letter **r** appears at positions 3, 8, and 9. So there are **3** “r”s.
2.7s94 output tokens

Debug This Error

I'm getting the following error in my Node.js application: TypeError: Cannot read properties of undefined (reading 'map') at UserList (/app/components/UserList.js:12:25) at renderWithHooks (/app/node_modules/rea…

GPT-6.1 Sol

The error means **`users` is `undefined` when `UserList` renders**. Calling `.map()` on `undefined` throws this error. This commonly happens when the parent doesn’t pass the `users` prop, or when data hasn’t finished loading yet. ### Fix: provide a default empty array ```jsx function UserList({ users = [] }) { return ( <ul> {users.map(user => ( <li key={user.id}>{user.name}</li> ))} </ul> ); } ``` This renders an empty list if `users` is omitted or `undefined`. It does **not** handle `null`. ### Check the parent component too Make sure it passes an array: ```jsx <UserList users={users} /> ``` If you’re fetching users asynchronously, initialize the stat…
5.8s306 output tokens

GPT-6 Luna

`users` is `undefined` when `UserList` renders, so calling `users.map(...)` throws. This often happens because the parent didn’t pass the prop or because data hasn’t loaded yet. If an empty list is acceptable until the data arrives, provide a default: ```jsx function UserList({ users = [] }) { return ( <ul> {users.map(user => ( <li key={user.id}>{user.name}</li> ))} </ul> ); } ``` Also check that the parent passes `users`: ```jsx <UserList users={users} /> ``` If `users` is loaded asynchronously, initialize it as an array: ```jsx const [users, setUsers] = useState([]); ``` If `null` is also possible, normalize it before mapping, for example `(users ?? […
3.8s289 output tokens

Code Review

Please review the following Python function and suggest improvements for readability, performance, and best practices: def get_data(url, retries=3): import requests import time for i in range(retries):…

GPT-6.1 Sol

The function is short, but its main weakness is that it hides failures: a network error, invalid JSON, and a genuinely empty result all return `[]`. ### Suggested improvements - **Move imports to module scope.** This is conventional and makes dependencies visible. Repeated imports are cached, so the performance benefit is minor. - **Avoid bare `except:`.** It catches everything, including `KeyboardInterrupt` and `SystemExit`, and can hide programming errors. - **Handle HTTP errors explicitly.** `raise_for_status()` provides useful exceptions. Retry transient failures such as timeouts, connection errors, HTTP 429, and HTTP 5xx—not permanent errors such as HTTP 404. - **Don’t sleep after the…
19.0s1094 output tokens

GPT-6 Luna

Key improvements: - Move imports to module scope. - Catch `requests.RequestException` instead of using a bare `except`; the current handler can hide programming errors as well as network failures. - Call `raise_for_status()` so unsuccessful HTTP responses are handled explicitly. - Use a list comprehension instead of building the result manually. - Replace `item["active"] == True` with `item.get("active") is True` if the field is expected to be the Boolean `True`. - Add backoff between attempts. A fixed two-second delay can make retries slower than necessary. - Decide whether failures should raise an exception or return `[]`. Returning `[]` makes a failed request indistinguishable from a suc…
16.5s1713 output tokens

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Frequently asked questions

Which is cheaper, GPT-6.1 Sol or GPT-6 Luna?
Per 1M output tokens, GPT-6.1 Sol is ¥1,787 and GPT-6 Luna is ¥89.35 on FastMetal (yen, before tax), so GPT-6 Luna is cheaper.
How do the context windows of GPT-6.1 Sol and GPT-6 Luna compare?
GPT-6.1 Sol takes 1,050,000 tokens; GPT-6 Luna takes 1,050,000.
Can I use GPT-6.1 Sol and GPT-6 Luna with the same API key?
Yes. On FastMetal's OpenAI-compatible endpoint, switch by passing "gpt-6.1-sol" or "gpt-6-luna" as the model. Each is billed at its own rate from the same prepaid balance.

Try both on one API key

Create an account and add credit to call GPT-6.1 Sol and GPT-6 Luna from the browser chat and the API. No monthly fee.

Create a free accountTry GPT-6.1 Sol in chatTry GPT-6 Luna in chat

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